/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.resource;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import reactor.core.publisher.Mono;

import org.springframework.cache.Cache;
import org.springframework.cache.CacheManager;
import org.springframework.core.io.Resource;
import org.springframework.util.Assert;
import org.springframework.web.server.ServerWebExchange;

/**
 * A {@link ResourceTransformer} that checks a {@link Cache} to see if a
 * previously transformed resource exists in the cache and returns it if found,
 * or otherwise delegates to the resolver chain and caches the result.
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 */
public class CachingResourceTransformer implements ResourceTransformer {

    private static final Log logger = LogFactory.getLog(CachingResourceTransformer.class);

    private final Cache cache;


    public CachingResourceTransformer(Cache cache) {
        Assert.notNull(cache, "Cache is required");
        this.cache = cache;
    }

    public CachingResourceTransformer(CacheManager cacheManager, String cacheName) {
        Cache cache = cacheManager.getCache(cacheName);
        if (cache == null) {
            throw new IllegalArgumentException("Cache '" + cacheName + "' not found");
        }
        this.cache = cache;
    }


    /**
     * Return the configured {@code Cache}.
     */
    public Cache getCache() {
        return this.cache;
    }


    @Override
    public Mono<Resource> transform(ServerWebExchange exchange, Resource resource,
                                    ResourceTransformerChain transformerChain) {

        Resource cachedResource = this.cache.get(resource, Resource.class);
        if (cachedResource != null) {
            if (logger.isTraceEnabled()) {
                logger.trace(exchange.getLogPrefix() + "Resource resolved from cache");
            }
            return Mono.just(cachedResource);
        }

        return transformerChain.transform(exchange, resource)
                .doOnNext(transformed -> this.cache.put(resource, transformed));
    }

}
